1. Field of the Invention
The present invention generally relates to an improved valve for use in the control of fluids in a pipeline. The valve of the present invention is particularly useful in providing a means of verifying that valve is shutting off fluids at both high and low pressures.
2. Description of Related Art
Ball valves, plug valves, and the like are well known to those skilled in the art. A common characteristic of these valves is that they may be moved from a full open position to a full closed position through an angle of not more than about ninety (90) degrees.
A simple ball valve comprises a rotatable ball having a bore therethrough corresponding to the fluid flow path, together with a seat for sealing with the ball surface. Ball valves permit fluid flow to be fully stopped by rotating the ball not more than about ninety (90) degrees. However, these valves offer only minimal graduated control of the fluid flow achieved by setting the ball at intermediate positions. Further, these valves are placed in the open or closed position without a mechanical force applied by the closure member against a seat.
A simple plug valve comprises a rotatable tapered plug having a bore therethrough disposed in a complementary housing. The plug permits flow to be fully stopped by rotating the plug more than about ninety (90) degrees. Plug valves operate similarly to the previously described ball valve and offer similar advantages and disadvantages.
Gate valves, globe valves and the like are also well known to those skilled in the art. A common characteristic of the valves is that they may be moved from a full open position to a full closed position by the rising and lowering of a valve stem acting on a closure member (gate in a gate valve or disc or plug in a globe valve). These valves offer sealing advantages over ball valves, but take longer to open or close and generally have a higher leakage of fluid to the atmosphere with the rising and lowering of the stem.
Ball, plug and gate valves all can include a feature or variation of design commonly called “double-block-and-bleed”. These valves have two seating surfaces which, in the closed position, block flow from both valve ends when the cavity between the seating surfaces is vented through a bleed connection provided on the body cavity. The seal between the seat and closure member occurs either at the exterior of a round surface or a flat surface, depending on valve type. The venting through a bleed connection provided on the body cavity permits verification that the valve is sealing or that the valve has leakage across one or more of the seating surfaces.
Another variation of design is called “double isolation block”, and is similar to a “double-block-and-bleed”. A double isolation block valve is a valve in which the body cavity is opened and the pressure is applied successively to each valve end and also to both the cavity and each end to demonstrate that no leakage is occurring in either the upstream seat or the downstream seat with pressure applied from either direction.
A valve offering significant advantages over conventional ball, plug, gate, and globe valves is the HEMIWEDGE® valve described in U.S. Pat. No. 4,962,911, and improved with a valve driver in U.S. Pat. No. 5,333,834, and improved with a cartridge feature for quick and easy repair in U.S. Pat. No. 7,357,145, the contents of which is incorporated by reference herein, and improved by method of manufacture in U.S. Pat. No. 7,484,523. The hemi-wedge valve includes a curved wedge comprising a tapered, spherical section rotatable through the fluid path and cooperating with a complementary curved seat to affect a shutoff. An important feature of the hemi-wedge valve is that the thickness of the wedge increases from its leading end to its trailing end when the valve is being closed. The wedge includes a bore forming a part of the fluid path through its thinner, leading end. The wedge is solid and thicker at its trailing end. Rotation of the hemi-wedge through about ninety (90) degrees into the fluid path closes the fluid path by blocking it with the solid and thicker end of the wedge. This provides a mechanical loading of the seat. Another important feature of the hemi-wedge valve is a replaceable cartridge which may be quickly and easily removed and replaced in a valve body without removing the valve from the pipeline.